Objective: Various practical methods have been used for pregnancy diagnosis in sheep. Methods of pregnancy diagnosis depending on visualization of the conceptus or determination of its secretory products in the maternal blood or in the milk are the most accurate and specific methods for pregnancy. In 1980, B-mode ultrasonography was introduced in the veterinary field and used for pregnancy diagnosis. Transrectal ultrasonography has been recommended as a simple, rapid and practical method for early pregnancy diagnosis in sheep. Methods: 40 clinically healthy Lori-Bakhtiari ewes aged between 2 to 8 years were used in this study. These ewes were estrus synchronized and inseminated and fertile rams were kept with the ewes for natural breeding. Transrectal ultrasonography was carried out in ewes. Results: The sensitivity of the test increased when performed at a more advanced stage of pregnancy. The sensitivity of the test increased in young ewes when scanning took place at a more advanced stage of pregnancy.